Stored-energy spring mechanisms for actuating high-voltage circuit breakers are known for example from DE 3408909 A1. The stored-energy spring mechanism described therein and formed as a hydraulic drive is housed together with a hydraulic store with a mechanical pressure-maintaining device in a common pressure housing, in which the conveying element for the hydraulic fluid, a high-pressure pump and also a control unit are integrated together with the appropriate hydraulic connections. The hydraulic store is intended to provide pressure energy to the hydraulic drive of the high-voltage circuit breaker without a further feed of outside energy and to actuate the drive in the intended manner, even in the event of a disruption or interruption of the energy feed.
In EP 0829892 A1, a stored-energy spring mechanism is described, with which a pre-loaded spring pressurizes a fluid via a pressure body and at least two pressure pistons. A drive rod of the stored-energy spring mechanism is moved by this fluid and is fastened on a drive piston that is slidingly displaceable in a working cylinder.
When assembling the stored-energy spring mechanism and during maintenance works, the hydraulic system of the stored-energy spring mechanism is pressureless. The pre-loaded spring is biased in this state and can be extended axially to the maximum. In so doing, the pre-loaded spring presses the pressure body against a stop on the cylinder housing, whereby the pressure body is fixed between the stop and the pre-loaded spring.
During operation of the stored-energy spring mechanism, the hydraulic system is under pressure. The pre-loaded spring is tensioned further in this state and its axial extension is reduced. In so doing, the pre-loaded spring presses the pressure body against the pressure piston, which thus pressurizes the fluid. The pressure body is fixed between the pressure piston and the pre-loaded spring.
Circuit breaker drives, which use disk springs in combination with a hydraulic piston as an energy store, are likewise known from DE 3408909 A1. The disk springs used for energy storage are compressed by a hydraulic piston, and a pressure/stroke characteristic curve of the piston, which is shown in FIG. 1b herein, can be derived from a force/stroke characteristic curve of the spring. Due to the degressive course of the force/stroke characteristic curve of the disk spring, the pressure change is therefore only weakly pronounced over a large part of the stroke of the piston.
As an alternative to the use of the relatively costly disk springs, there is generally the possibility of using other spring types, such as coil springs, which are of simple structure and therefore more cost effective. Due to the wide distribution and simple manufacture, coil springs are more easily obtainable on the market compared to disk springs.
In a favorable case, these coil springs can have a linear force/stroke characteristic curve as is illustrated in FIG. 1c herein, wherein this characteristic curve can even transition into a progressive characteristic curve in the unfavorable case. This characteristic curve could also be translated accordingly again into a pressure/stroke characteristic curve of the piston and have a strong pressure change over the stroke. This behavior can be less desirable for hydraulic drives of high-voltage circuit breakers, caused by the strong pressure change over the stroke, and compared to the degressive characteristic curve occurring with disk springs can lead to a strong pressure change over the storage stroke of the pressure piston of the energy store.